1. Field of the Invention
The present invention relates to an optical transmission apparatus for receiving a wave division multiplexed (WDM) light or an optical amplifier for relaying light between optical transmission apparatuses.
2. Description of the Related Art
Demands for wave division multiplex (WDM) transmission apparatuses are growing in recent years against the background of increased communication traffic. WDM transmission apparatuses have been actively introduced not only as optical repeating nodes in backbone networks, but also to local networks. Thus many optical add drop multiplexers (OADM) are arranged in a network.
A deviation of levels between wavelengths within a signal band occurs in these WDM network systems due to wavelength dependent losses (WDL) of fiber, stimulated Raman scattering (SRS), which is a nonlinear effect of fiber, WDL of various optical components within a node and the like.
Such a deviation of levels causes deterioration of the optical signal-to-noise ratio (OSNR) of light in a receiver input part, as well as deterioration of the dynamic range of light input and the transmission characteristics of a system.
Uniform and linear tilt corrections are conventionally made to tilt generated in each transmission path fiber to improve the transmission characteristics of a system.
The conventional tilt correction method makes uniform and linear tilt corrections in a relay amplifier for each transmission path fiber. However, appropriate tilt corrections are sometimes not realized because tilt may be generated as a difference from tilt correction amounts due to the distance of transmission path fiber, WDL, loss factor, different effective sectional area for each fiber type, transmission wavelength number and the like.
Such tilt accumulates when the system is viewed as a whole. Therefore, it is necessary to appropriately correct tilt generated in each transmission path fiber to improve OSNR in a receiver and level diagrams in a node, for the purpose of improving transmission characteristics of the system.